Golf ball

ABSTRACT

L1 represents a ratio of a lift coefficient CL1 relative to a drag coefficient CD1, the lift coefficient CL1 and the drag coefficient CD1 being measured under conditions of a Reynolds number of 1.290×105 and a spin rate of 2820 rpm. L2 represents a ratio of a lift coefficient CL2 relative to a drag coefficient CD2, the lift coefficient CL2 and the drag coefficient CD2 being measured under conditions of a Reynolds number of 1.771×105 and a spin rate of 2940 rpm.

CROSS REFERENCE PARAGRAPH

This application is a Continuation of U.S. application Ser. No.14/788,311, filed on Jun. 30, 2015, which claims priority to PatentApplication No. 2014-133826 filed in JAPAN on Jun. 30, 2014, all ofwhich are hereby incorporated by reference.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to golf balls. Specifically, the presentinvention relates to improvement of aerodynamic characteristics of golfballs.

Description of the Related Art

Golf balls have a large number of dimples on the surfaces thereof. Thedimples disturb the air flow around the golf ball during flight to causeturbulent flow separation. This phenomenon is referred to as“turbulization”. Due to the turbulization, separation points of the airfrom the golf ball shift backwards leading to a reduction of drag. Theturbulization promotes the displacement between the separation point onthe upper side and the separation point on the lower side of the golfball, which results from the backspin, thereby enhancing the lift forcethat acts upon the golf ball. Excellent dimples efficiently disturb theair flow. The excellent dimples produce a long flight distance.

A golf player can select the brand of a golf ball to be used by the golfplayer. In a golf tournament, the brand of a golf ball used by a golfplayer is often different from that of another golf player. In thisrespect, golf is a unique ball game.

Golf should be a sport in which golf players compete with each other ontheir skills. It is not preferable that scores of golf players greatlydepend on the brands of golf balls. In this respect, the United StatesGolf Association (USGA) has established various rules aboutcharacteristics of golf balls. For example, rules about weight,diameter, initial speed, flight distance, and symmetry have beenestablished.

Various golf balls have been proposed which can satisfy golf playerswhile conforming to the rules.

JPH5-103846 discloses a golf ball which has dimples the diameters, thedepths, and the number of which are made appropriate.

U.S. Pat. No. 5,782,703 (JPH10-43342) discloses a golf ball which hasdimples the ratio of the diameter and the depth of each of which is madeappropriate.

U.S. Pat. No. 5,782,702 (JPH10-43343) discloses a golf ball in which theratio of the volumes of dimples relative to the volume of the ball ismade appropriate.

JP2000-107338 discloses a golf ball having a diameter and a weight whichare made appropriate.

Technological innovation in golf ball and golf club is remarkable. Inrecent tour tournaments, the average flight distance at tee shots hasbeen increasing. The large flight distance makes a second shot easy. Thelarge flight distance impairs the public interest in tournaments.

The USGA is scheduled to change the rules about flight distance. Thehead speeds of professional golf players who participate in tournamentsare high. The USGA will strengthen regulations on a flight distance uponhitting at a high head speed.

Meanwhile, there are no regulations on a flight distance upon hitting ata low head speed. Amateur golf players desire longer flight distances. Agolf ball is desired which achieves a long flight distance when beinghit at a low head speed while conforming to the rules of the USGA.

For golf players, in addition to flight distance, feeling is alsoimportant. Golf players place importance on hit feeling and trajectoryfeeling. Golf players prefer soft hit feeling. Furthermore, golf playersprefer high trajectories.

An object of the present invention is to provide a golf ball whichsatisfies a golf player having a low head speed.

SUMMARY OF THE INVENTION

A golf ball according to the present invention includes a core and acover positioned outside the core. The golf ball has a large number ofdimples on a surface thereof. The cover has a Shore D hardness of equalto or greater than 30 but equal to or less than 50. The golf ball has anamount of compressive deformation of equal to or greater than 3.0 mm butequal to or less than 5.0 mm, the amount of compressive deformationbeing measured under conditions of an initial load of 98 N and a finalload of 1274 N. The golf ball meets the following mathematical formula(I):

0.80≤((L1+L2)/2)≤0.95  (I),

where: L1 represents a ratio (CL1/CD1) of a lift coefficient CL1relative to a drag coefficient CD1, the lift coefficient CL1 and thedrag coefficient CD1 being measured under conditions of a Reynoldsnumber of 1.290×105 and a spin rate of 2820 rpm; and L2 represents aratio (CL2/CD2) of a lift coefficient CL2 relative to a drag coefficientCD2, the lift coefficient CL2 and the drag coefficient CD2 beingmeasured under conditions of a Reynolds number of 1.771×105 and a spinrate of 2940 rpm.

When the golf ball according to the present invention is hit by a golfplayer having a low head speed, a sufficient flight distance isachieved. The golf ball provides preferable feeling to the golf playerhaving a low head speed.

Preferably, a total volume of the dimples is equal to or greater than430 mm3 but equal to or less than 580 mm3.

Preferably, the cover has a thickness of equal to or greater than 0.3 mmbut equal to or less than 1.8 mm.

Preferably, the ratio L1 is equal to or greater than 0.85 but equal toor less than 0.93. Preferably, the ratio L2 is equal to or greater than0.76 but equal to or less than 0.92.

Preferably, a ratio of a sum of spherical surface areas of the dimplesrelative to a surface area of a phantom sphere of the golf ball is equalto or greater than 0.780 but equal to or less than 0.950.

Preferably, a total number of the dimples is equal to or greater than250 but equal to or less than 450.

Preferably, each dimple has a diameter Dm of equal to or greater than2.0 mm but equal to or less than 6.0 mm.

Preferably, each dimple has a depth of equal to or greater than 0.10 mmbut equal to or less than 0.60 mm.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of a golf ball according to oneembodiment of the present invention;

FIG. 2 is an enlarged front view of the golf ball in FIG. 1;

FIG. 3 is a plan view of the golf ball in FIG. 2; and

FIG. 4 is a partially enlarged cross-sectional view of the golf ball inFIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following will describe in detail the present invention, based onpreferred embodiments with reference to the accompanying drawings.

FIG. 1 is a partially cutaway cross-sectional view of a golf ball 2according to one embodiment of the present invention. The golf ball 2includes a spherical core 4 and a cover 6 positioned outside the core 4.The core 4 includes a spherical center 8 and a mid layer 10 positionedoutside the center 8. The golf ball 2 includes a paint layer and a marklayer on the external side of the cover 6 although these layers are notshown in the drawing. Furthermore, the golf ball 2 has a large number ofdimples 12 on the surface thereof. Of the surface of the golf ball 2,the part other than the dimples 12 is a land 14. The golf ball 2 mayinclude another layer between the center 8 and the mid layer 10. Thegolf ball 2 may include another layer between the mid layer 10 and thecover 6.

The golf ball 2 preferably has a diameter of equal to or greater than 40mm but equal to or less than 45 mm. From the standpoint of conformity tothe rules established by the United States Golf Association (USGA), thediameter is particularly preferably equal to or greater than 42.67 mm.In light of suppression of air resistance, the diameter is morepreferably equal to or less than 44 mm and particularly preferably equalto or less than 42.80 mm. The golf ball 2 preferably has a weight ofequal to or greater than 40 g but equal to or less than 50 g. In lightof attainment of great inertia, the weight is more preferably equal toor greater than 44 g and particularly preferably equal to or greaterthan 45.00 g. From the standpoint of conformity to the rules establishedby the USGA, the weight is particularly preferably equal to or less than45.93 g.

The center 8 is obtained by crosslinking a rubber composition. Examplesof preferable base rubbers for use in the rubber composition includepolybutadienes, polyisoprenes, styrene-butadiene copolymers,ethylene-propylene-diene copolymers, and natural rubbers. In light ofresilience performance, polybutadienes are preferred. When apolybutadiene and another rubber are used in combination, it ispreferred if the polybutadiene is a principal component. Specifically,the proportion of the polybutadiene to the entire base rubber ispreferably equal to or greater than 50% by weight and particularlypreferably equal to or greater than 80% by weight. A polybutadiene inwhich the proportion of cis-1,4 bonds is equal to or greater than 80% isparticularly preferred.

The rubber composition of the center 8 preferably includes aco-crosslinking agent. Preferable co-crosslinking agents in light ofresilience performance are monovalent or bivalent metal salts of anα,β-unsaturated carboxylic acid having 2 to 8 carbon atoms. Examples ofpreferable co-crosslinking agents include zinc acrylate, magnesiumacrylate, zinc methacrylate, and magnesium methacrylate. In light ofresilience performance, zinc acrylate and zinc methacrylate areparticularly preferred.

The rubber composition may include a metal oxide and an α,β-unsaturatedcarboxylic acid having 2 to 8 carbon atoms. They both react with eachother in the rubber composition to obtain a salt. The salt serves as aco-crosslinking agent. Examples of preferable α,β-unsaturated carboxylicacids include acrylic acid and methacrylic acid. Examples of preferablemetal oxides include zinc oxide and magnesium oxide.

In light of resilience performance of the golf ball 2, the amount of theco-crosslinking agent per 100 parts by weight of the base rubber ispreferably equal to or greater than 10 parts by weight and particularlypreferably equal to or greater than 15 parts by weight. In light of softfeel at impact, the amount is preferably equal to or less than 50 partsby weight and particularly preferably equal to or less than 45 parts byweight.

Preferably, the rubber composition of the center 8 includes an organicperoxide together with the co-crosslinking agent. The organic peroxideserves as a crosslinking initiator. The organic peroxide contributes tothe resilience performance of the golf ball 2. Examples of suitableorganic peroxides include dicumyl peroxide,1,1-bis(t-butylperoxy)-3,3,5-trimethylcyclohexane,2,5-dimethyl-2,5-di(t-butylperoxy)hexane, and di-t-butyl peroxide. Anorganic peroxide with particularly high versatility is dicumyl peroxide.

In light of resilience performance of the golf ball 2, the amount of theorganic peroxide per 100 parts by weight of the base rubber ispreferably equal to or greater than 0.1 parts by weight, more preferablyequal to or greater than 0.3 parts by weight, and particularlypreferably equal to or greater than 0.5 parts by weight. In light ofsoft feel at impact, the amount is preferably equal to or less than 3.0parts by weight, more preferably equal to or less than 2.8 parts byweight, and particularly preferably equal to or less than 2.5 parts byweight.

Preferably, the rubber composition of the center 8 includes an organicsulfur compound. Examples of preferable organic sulfur compounds includemonosubstitutions such as diphenyl disulfide,bis(4-chlorophenyl)disulfide, bis(3-chlorophenyl)disulfide,bis(4-bromophenyl)disulfide, bis(3-bromophenyl)disulfide,bis(4-fluorophenyl)disulfide, bis(4-iodophenyl)disulfide, andbis(4-cyanophenyl)disulfide; disubstitutions such asbis(2,5-dichlorophenyl)disulfide, bis(3,5-dichlorophenyl)disulfide,bis(2,6-dichlorophenyl)disulfide, bis(2,5-dibromophenyl)disulfide,bis(3,5-dibromophenyl)disulfide, bis(2-chloro-5-bromophenyl)disulfide,and bis(2-cyano-5-bromophenyl)disulfide; trisubstitutions such asbis(2,4,6-trichlorophenyl)disulfide andbis(2-cyano-4-chloro-6-bromophenyl)disulfide; tetrasubstitutions such asbis(2,3,5,6-tetrachlorophenyl)disulfide; and pentasubstitutions such asbis(2,3,4,5,6-pentachlorophenyl)disulfide andbis(2,3,4,5,6-pentabromophenyl)disulfide. The organic sulfur compoundcontributes to resilience performance. Particularly preferable organicsulfur compounds are diphenyl disulfide andbis(pentabromophenyl)disulfide.

In light of resilience performance of the golf ball 2, the amount of theorganic sulfur compound per 100 parts by weight of the base rubber ispreferably equal to or greater than 0.1 parts by weight and particularlypreferably equal to or greater than 0.2 parts by weight. In light ofsoft feel at impact, the amount is preferably equal to or less than 1.5parts by weight, more preferably equal to or less than 1.0 parts byweight, and particularly preferably equal to or less than 0.8 parts byweight.

For the purpose of adjusting specific gravity and the like, a filler maybe included in the center 8. Examples of suitable fillers include zincoxide, barium sulfate, calcium carbonate, and magnesium carbonate.Powder of a metal with a high specific gravity may be included as afiller. Specific examples of metals with a high specific gravity includetungsten and molybdenum. The amount of the filler is determined asappropriate so that the intended specific gravity of the center 8 isaccomplished. A particularly preferable filler is zinc oxide. Zinc oxideserves not only as a specific gravity adjuster but also as acrosslinking activator. According to need, various additives such assulfur, an anti-aging agent, a coloring agent, a plasticizer, adispersant, and the like are included in the rubber composition of thecenter 8 in an adequate amount. Crosslinked rubber powder or syntheticresin powder may also be included in the center 8.

The center 8 preferably has a surface hardness H1 of equal to or greaterthan 35 but equal to or less than 60. The center 8 having a surfacehardness H1 of equal to or greater than 35 can achieve excellentresilience performance. In this respect, the surface hardness H1 is morepreferably equal to or greater than 40 and particularly preferably equalto or greater than 45. The center 8 having a surface hardness H1 ofequal to or less than 60 can achieve excellent feel at impact. In thisrespect, the surface hardness H1 is more preferably equal to or lessthan 55 and particularly preferably equal to or less than 50. Thesurface hardness H1 is measured by pressing a Shore D type hardnessscale against the surface of the center 8 from which the mid layer 10and the cover 6 have been removed. For the measurement, an automatedrubber hardness measurement machine (trade name “P1”, manufactured byKobunshi Keiki Co., Ltd.), to which this hardness scale is mounted, isused.

In light of feel at impact, the center 8 has an amount of compressivedeformation DF1 of preferably equal to or greater than 3.5 mm, morepreferably equal to or greater than 4.0 mm, and particularly preferablyequal to or greater than 4.5 mm. In light of resilience performance, theamount of compressive deformation DF1 is preferably equal to or lessthan 6.5 mm, more preferably equal to or less than 6.0 mm, andparticularly preferably equal to or less than 5.5 mm.

For measurement of the amount of compressive deformation, a YAMADA typecompression tester is used. In the tester, a sphere (the center 8, thecore 4, the golf ball 2, etc.) which is an object to be measured isplaced on a hard plate made of metal. Next, a cylinder made of metalgradually descends toward the sphere. The sphere, squeezed between thebottom face of the cylinder and the hard plate, becomes deformed. Amigration distance of the cylinder, starting from the state in which aninitial load of 98 N is applied to the sphere up to the state in which afinal load of 1274 N is applied thereto, is measured. A moving speed ofthe cylinder until the initial load is applied is 0.83 mm/s. A movingspeed of the cylinder after the initial speed is applied until the finalload is applied is 1.67 mm/s. The atmospheric temperature at themeasurement is 23° C. Prior to the measurement, the sphere is kept in athermostat bath at 23° C. for 24 hours or longer.

The center 8 preferably has a diameter of equal to or greater than 35.0mm but equal to or less than 40.0 mm. The center 8 preferably has aweight of equal to or greater than 30 g but equal to or less than 41 g.The temperature for crosslinking the center 8 is equal to or higher than140° C. but equal to or lower than 180° C. The time period forcrosslinking the center 8 is equal to or longer than 10 minutes butequal to or shorter than 60 minutes. The center 8 may include two ormore layers. The center 8 may have a rib on the surface thereof. Thecenter 8 may be hollow.

The mid layer 10 is formed from a thermoplastic resin composition.Examples of the base polymer of the resin composition include ionomerresins, thermoplastic polyester elastomers, thermoplastic poly amideelastomers, thermoplastic polyurethane elastomers, thermoplasticpolyolefin elastomers, and thermoplastic polystyrene elastomers. Ionomerresins are particularly preferred. Ionomer resins are highly elastic. Asdescribed later, the cover 6 of the golf ball 2 is thin. When the golfball 2 is hit, the mid layer 10 significantly deforms due to thethinness of the cover 6. Therefore, the mid layer 10 greatly influencesresilience performance. The golf ball 2 which includes the mid layer 10including an ionomer resin has excellent resilience performance.

An ionomer resin and another resin may be used in combination. In thiscase, in light of resilience performance, the ionomer resin is includedas the principal component of the base polymer. The proportion of theionomer resin to the entire base polymer is preferably equal to orgreater than 50% by weight, more preferably equal to or greater than 70%by weight, and particularly preferably equal to or greater than 85% byweight.

Examples of preferable ionomer resins include binary copolymers formedwith an α-olefin and an α,β-unsaturated carboxylic acid having 3 to 8carbon atoms. A preferable binary copolymer includes 80% by weight ormore but 90% by weight or less of an α-olefin, and 10% by weight or morebut 20% by weight or less of an α,β-unsaturated carboxylic acid. Thebinary copolymer has excellent resilience performance. Examples of otherpreferable ionomer resins include ternary copolymers formed with: anα-olefin; an α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms;and an α,β-unsaturated carboxylate ester having 2 to 22 carbon atoms. Apreferable ternary copolymer includes 70% by weight or more but 85% byweight or less of an α-olefin, 5% by weight or more but 30% by weight orless of an α,β-unsaturated carboxylic acid, and 1% by weight or more but25% by weight or less of an α,β-unsaturated carboxylate ester. Theternary copolymer has excellent resilience performance. For the binarycopolymer and the ternary copolymer, preferable α-olefins are ethyleneand propylene, while preferable α,β-unsaturated carboxylic acids areacrylic acid and methacrylic acid. A particularly preferable ionomerresin is a copolymer formed with ethylene and acrylic acid. Anotherparticularly preferable ionomer resin is a copolymer formed withethylene and methacrylic acid.

In the binary copolymer and the ternary copolymer, some of the carboxylgroups are neutralized with metal ions. Examples of metal ions for usein neutralization include sodium ion, potassium ion, lithium ion, zincion, calcium ion, magnesium ion, aluminum ion, and neodymium ion. Theneutralization may be carried out with two or more types of metal ions.Particularly suitable metal ions in light of resilience performance anddurability of the golf ball 2 are sodium ion, zinc ion, lithium ion, andmagnesium ion.

Specific examples of ionomer resins include trade names “Himilan 1555”,“Himilan 1557”, “Himilan 1605”, “Himilan 1706”, “Himilan 1707”, “Himilan1856”, “Himilan 1855”, “Himilan AM7311”, “Himilan AM7315”, “HimilanAM7317”, “Himilan AM7329”, and “Himilan AM7337”, manufactured by DuPont-MITSUI POLYCHEMICALS Co., Ltd.; trade names “Surlyn 6120”, “Surlyn6910”, “Surlyn 7930”, “Surlyn 7940”, “Surlyn 8140”, “Surlyn 8150”,“Surlyn 8940”, “Surlyn 8945”, “Surlyn 9120”, “Surlyn 9150”, “Surlyn9910”, “Surlyn 9945”, “Surlyn AD8546”, “HPF1000”, and “HPF2000”,manufactured by E.I. du Pont de Nemours and Company; and trade names“IOTEK 7010”, “IOTEK 7030”, “IOTEK 7510”, “IOTEK 7520”, “IOTEK 8000”,and “IOTEK 8030”, manufactured by ExxonMobil Chemical Corporation. Twoor more ionomer resins may be used in combination.

For the purpose of adjusting specific gravity and the like, a filler maybe included in the resin composition of the mid layer 10. Examples ofsuitable fillers include zinc oxide, barium sulfate, calcium carbonate,and magnesium carbonate. Powder of a metal with a high specific gravitymay be included as a filler. Specific examples of metals with a highspecific gravity include tungsten and molybdenum. The amount of thefiller is determined as appropriate so that the intended specificgravity of the mid layer 10 is accomplished. A coloring agent,crosslinked rubber powder, or synthetic resin powder may also beincluded in the mid layer 10.

The mid layer 10 has a thickness of preferably equal to or greater than0.5 mm and more preferably equal to or greater than 1.0 mm. Thethickness is preferably equal to or less than 2.0 mm and more preferablyequal to or less than 1.8 mm.

The mid layer 10 has a hardness H2 of preferably equal to or greaterthan 55, more preferably equal to or greater than 60, and particularlypreferably equal to or greater than 63. The hardness H2 is preferablyequal to or less than 75, more preferably equal to or less than 72, andparticularly preferably equal to or less than 70.

In the present invention, the hardness H2 of the mid layer 10 and ahardness H3 of the cover 6 are measured according to the standards of“ASTM-D 2240-68”. For the measurement, an automated rubber hardnessmeasurement machine (trade name “P1”, manufactured by Kobunshi KeikiCo., Ltd.), to which a Shore D type hardness scale is mounted, is used.For the measurement, a sheet that is formed by hot press, is formed fromthe same material as that of the mid layer 10 (or the cover 6), and hasa thickness of about 2 mm is used. Prior to the measurement, a sheet iskept at 23° C. for two weeks. At the measurement, three sheets arestacked.

The core 4 (i.e., the center 8 and the mid layer 10) preferably has adiameter of equal to or greater than 41.0 mm but equal to or less than42.0 mm. The core 4 preferably has a weight of equal to or greater than42.0 g but equal to or less than 44.0 g. The core 4 preferably has anamount of compressive deformation DF2 of equal to or greater than 3.0 mmbut equal to or less than 5.0 mm.

The cover 6 is formed from a resin composition. Examples of the baseresin of the resin composition include polyurethanes, polyamideelastomers, styrene block-containing thermoplastic elastomers, polyesterelastomers, polyolefin elastomers, and ionomer resins.

A preferable base polymer is a polyurethane. The resin composition mayinclude a thermoplastic polyurethane, or may include a thermosettingpolyurethane. In light of productivity, the thermoplastic polyurethaneis preferable. The thermoplastic polyurethane includes a polyurethanecomponent as a hard segment, and a polyester component or a polyethercomponent as a soft segment. The thermoplastic polyurethane is flexible.The cover 6 in which the polyurethane is used has excellent scuffresistance. When a thermoplastic polyurethane and another resin are usedin combination for the cover 6, the proportion of the thermoplasticpolyurethane to the entire base resin is preferably equal to or greaterthan 50% by weight, more preferably equal to or greater than 60% byweight, and particularly preferably equal to or greater than 70% byweight.

The thermoplastic polyurethane has a urethane bond within the molecule.The urethane bond can be formed by reacting a polyol with apolyisocyanate. The polyol, as a material for the urethane bond, has aplurality of hydroxyl groups. Low-molecular-weight polyols andhigh-molecular-weight polyols can be used.

Examples of low-molecular-weight polyols include diols, triols,tetraols, and hexaols. Specific examples of diols include ethyleneglycol, diethylene glycol, triethylene glycol, 1,2-propanediol,1,3-propanediol, 2-methyl-1,3-propanediol, dipropylene glycol,1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 2,3-butanediol,2,3-dimethyl-2,3-butanediol, neopentyl glycol, pentanediol, hexanediol,heptanediol, octanediol, and 1,6-cyclohexanedimethylol. Aniline-baseddiols or bisphenol A-based diols may be used. Specific examples oftriols include glycerin, trimethylol propane, and hexanetriol. Specificexamples of tetraols include pentaerythritol and sorbitol.

Examples of high-molecular-weight polyols include polyether polyols suchas polyoxyethylene glycol (PEG), polyoxypropylene glycol (PPG), andpolytetramethylene ether glycol (PTMG); condensed polyester polyols suchas polyethylene adipate (PEA), polybutylene adipate (PBA), andpolyhexamethylene adipate (PHMA); lactone polyester polyols such aspoly-ε-caprolactone (PCL); polycarbonate polyols such aspolyhexamethylene carbonate; and acrylic polyols. Two or more polyolsmay be used in combination. In light of feel at impact of the golf ball2, the high-molecular-weight polyol has a number average molecularweight of preferably equal to or greater than 400 and more preferablyequal to or greater than 1000. The number average molecular weight ispreferably equal to or less than 10000.

Examples of polyisocyanates, as a material for the urethane bond,include aromatic diisocyanates, alicyclic diisocyanates, and aliphaticdiisocyanates. Two or more types of diisocyanates may be used incombination.

Examples of aromatic diisocyanates include 2,4-toluene diisocyanate,2,6-toluene diisocyanate, 4,4′-diphenylmethane diisocyanate (MDI),1,5-naphthylene diisocyanate (NDI), 3,3′-bitolylene-4,4′-diisocyanate(TODI), xylylene diisocyanate (XDI), tetramethylxylylene diisocyanate(TMXDI), and paraphenylene diisocyanate (PPDI). One example of aliphaticdiisocyanates is hexamethylene diisocyanate (HDI). Examples of alicyclicdiisocyanates include 4,4′-dicyclohexylmethane diisocyanate (H12MDI),1,3-bis(isocyanatemethyl)cyclohexane (H6XDI), isophorone diisocyanate(IPDI), and trans-1,4-cyclohexane diisocyanate (CHDI).4,4′-dicyclohexylmethane diisocyanate is preferable.

Specific examples of the thermoplastic polyurethane include trade names“Elastollan XNY80A”, “Elastollan XNY82A”, “Elastollan XNY85A”,“Elastollan XNY90A”, “Elastollan XNY97A”, “Elastollan XNY585”, and“Elastollan XKP016N”, manufactured by BASF Japan Ltd.; and trade names“RESAMINE P4585LS” and “RESAMINE PS62490”, manufactured by DainichiseikaColor & Chemicals Mfg. Co., Ltd.

According to need, a coloring agent such as titanium dioxide, a fillersuch as barium sulfate, a dispersant, an antioxidant, an ultravioletabsorber, a light stabilizer, a fluorescent material, a fluorescentbrightener, and the like are included in the resin composition of thecover 6 in an adequate amount.

The cover 6 preferably has a hardness H3 of equal to or greater than 30but equal to or less than 50. The golf ball 2 having a hardness H3 ofequal to or greater than 30 has excellent resilience performance. Whenthe golf ball 2 is hit by an amateur golf player, a long flight distanceis achieved. In this respect, the hardness H3 is more preferably equalto or greater than 31 and particularly preferably equal to or greaterthan 32. The golf ball 2 having a hardness H3 of equal to or less than50 has excellent spin performance. The spin achieves a high trajectoryof the golf ball 2. When the golf ball 2 is hit by an amateur golfplayer, excellent trajectory feeling is obtained. In this respect, thehardness H3 is more preferably equal to or less than 45 and particularlypreferably equal to or less than 40.

The cover 6 preferably has a thickness of equal to or greater than 0.3mm but equal to or less than 1.8 mm. The golf ball 2 in which thethickness of the cover 6 is equal to or greater than 0.3 mm hasexcellent spin performance. The spin achieves a high trajectory of thegolf ball 2. When the golf ball 2 is hit by an amateur golf player,excellent trajectory feeling is obtained. In this respect, the thicknessis more preferably equal to or greater than 0.4 mm and particularlypreferably equal to or greater than 0.5 mm. The golf ball 2 in which thethickness is equal to or less than 1.8 mm has excellent resilienceperformance. When the golf ball 2 is hit by an amateur golf player, along flight distance is achieved. Furthermore, the golf ball 2 in whichthe thickness of the cover 6 is equal to or less than 1.8 mm isexcellent in hit feeling. In these respects, the thickness is morepreferably equal to or less than 1.0 mm and particularly preferablyequal to or less than 0.8 mm.

The golf ball 2 may include a reinforcing layer between the mid layer 10and the cover 6. The reinforcing layer firmly adheres to the mid layer10 and also to the cover 6. The reinforcing layer suppresses separationof the mid layer 10 from the cover 6. The reinforcing layer is formedfrom a resin composition. Examples of a preferable base polymer of thereinforcing layer include two-component curing type epoxy resins andtwo-component curing type urethane resins.

The golf ball 2 has an amount of compressive deformation DF3 of equal toor greater than 3.0 mm but equal to or less than 5.0 mm. The golf ball 2having an amount of compressive deformation DF3 of equal to or greaterthan 3.0 mm does not have excessive resilience performance. The golfball 2 can conform to the rules about flight distance established by theUSGA. Furthermore, with the golf ball 2 having an amount of compressivedeformation DF3 of equal to or greater than 3.0 mm, soft hit feeling isobtained. In these respects, the amount of compressive deformation DF3is more preferably equal to or greater than 3.5 mm and particularlypreferably equal to or greater than 3.8 mm. The golf ball 2 having anamount of compressive deformation DF3 of equal to or less than 5.0 mmhas excellent resilience performance. In this respect, the amount ofcompressive deformation DF3 is more preferably equal to or less than 4.7mm and particularly preferably equal to or less than 4.5 mm.

As shown in FIGS. 2 and 3, the contour of each dimple 12 is circular.The golf ball 2 has dimples A each having a diameter of 4.6 mm; dimplesB each having a diameter of 4.4 mm; dimples C each having a diameter of4.2 mm; dimples D each having a diameter of 4.0 mm; dimples E eachhaving a diameter of 3.9 mm; and dimples F each having a diameter of 2.6mm. The number of types of the dimples 12 is six. The golf ball 2 mayhave non-circular dimples instead of the circular dimples 12 or togetherwith circular dimples 12.

The number of the dimples A is 42; the number of the dimples B is 72;the number of the dimples C is 66; the number of the dimples D is 126;the number of the dimples E is 12; and the number of the dimples F is12. The total number of the dimples 12 is 330.

FIG. 4 shows a cross section along a plane passing through the center ofthe dimple 12 and the center of the golf ball 2. In FIG. 4, thetop-to-bottom direction is the depth direction of the dimple 12. In FIG.4, a chain double-dashed line indicates a phantom sphere 16. The surfaceof the phantom sphere 16 is the surface of the golf ball 2 when it ispostulated that no dimple 12 exists. The dimple 12 is recessed from thesurface of the phantom sphere 16. The land 14 coincides with the surfaceof the phantom sphere 16. In the present embodiment, the cross-sectionalshape of each dimple 12 is substantially a circular arc.

In FIG. 4, a double ended arrow Dm indicates the diameter of the dimple12. The diameter Dm is the distance between two tangent points Edappearing on a tangent line Tg that is drawn tangent to the far oppositeends of the dimple 12. Each tangent point Ed is also the edge of thedimple 12. The edge Ed defines the contour of the dimple 12. In FIG. 4,a double ended arrow Dp indicates the depth of the dimple 12. The depthDp is the distance between the deepest part of the dimple 12 and thephantom sphere 16.

The diameter Dm of each dimple 12 is preferably equal to or greater than2.0 mm but equal to or less than 6.0 mm. The dimple 12 having a diameterDm of equal to or greater than 2.0 mm contributes to turbulization. Inthis respect, the diameter Dm is more preferably equal to or greaterthan 2.5 mm and particularly preferably equal to or greater than 2.8 mm.The dimple 12 having a diameter Dm of equal to or less than 6.0 mm doesnot impair a fundamental feature of the golf ball 2 that the golf ball 2is substantially a sphere. In this respect, the diameter Dm is morepreferably equal to or less than 5.5 mm and particularly preferablyequal to or less than 5.0 mm.

In light of suppression of rising of the golf ball 2 during flight, thedepth Dp of each dimple 12 is preferably equal to or greater than 0.10mm, more preferably equal to or greater than 0.13 mm, and particularlypreferably equal to or greater than 0.15 mm. In light of suppression ofdropping of the golf ball 2 during flight, the depth Dp is preferablyequal to or less than 0.60 mm, more preferably equal to or less than0.55 mm, and particularly preferably equal to or less than 0.50 mm.

The spherical surface area s of each dimple 12 is the area of a zonesurrounded by the contour line of the dimple 12, of the surface of thephantom sphere 16 of the golf ball 2. In the golf ball 2 shown in FIGS.2 and 3, the spherical surface area s of each dimple A is 16.61 mm2; thespherical surface area s of each dimple B is 15.20 mm2; the sphericalsurface area s of each dimple C is 13.85 mm2; the spherical surface areas of each dimple D is 12.56 mm2; the spherical surface area s of eachdimple E is 11.94 mm2; and the spherical surface areas of each dimple Fis 5.31 mm2.

The ratio of the sum of the spherical surface areas s of all the dimples12 to the surface area of the phantom sphere 16 is referred to as anoccupation ratio. In light of turbulization, the occupation ratio ispreferably equal to or greater than 0.780, more preferably equal to orgreater than 0.800, and particularly preferably equal to or greater than0.840. The occupation ratio is preferably equal to or less than 0.950.In the golf ball 2 shown in FIGS. 2 and 3, the sum of the sphericalsurface areas s is 4495.3 mm2. The surface area of the phantom sphere 16of the golf ball 2 is 5728.0 mm2, and thus the occupation ratio is0.785.

From the standpoint that a sufficient occupation ratio is achieved, thetotal number of the dimples 12 is preferably equal to or greater than250, more preferably equal to or greater than 280, and particularlypreferably equal to or greater than 300. From the standpoint that eachdimple 12 can contribute to turbulization, the total number of thedimples 12 is preferably equal to or less than 450, more preferablyequal to or less than 400, and particularly preferably equal to or lessthan 380.

In the present invention, the “volume of the dimple” means the volume ofa portion surrounded by the phantom sphere 16 and the surface of thedimple 12. The total volume of the dimples 12 of the golf ball 2 ispreferably equal to or less than 580 mm3. With the golf ball 2 in whichthe total volume is equal to or less than 580 mm3, a high trajectory isachieved. When the golf ball 2 is hit by an amateur golf player,excellent trajectory feeling is obtained. In this respect, the totalvolume is more preferably equal to or less than 560 mm3 and particularlypreferably equal to or less than 550 mm3. In light of suppression ofrising of the golf ball 2 during flight, the total volume is preferablyequal to or greater than 430 mm3.

The golf ball 2 meets the following mathematical formula (I):

0.80≤((L1+L2)/2)≤0.95  (I),

where: L1 represents the ratio (CL1/CD1) of a lift coefficient CL1relative to a drag coefficient CD1, the lift coefficient CL1 and thedrag coefficient CD1 being measured under conditions of a Reynoldsnumber of 1.290×105 and a spin rate of 2820 rpm; and L2 represents theratio (CL2/CD2) of a lift coefficient CL2 relative to a drag coefficientCD2, the lift coefficient CL2 and the drag coefficient CD2 beingmeasured under conditions of a Reynolds number of 1.771×105 and a spinrate of 2940 rpm. The lift coefficients and the drag coefficients aremeasured according to the Indoor Test Range (ITR) determined by theUSGA.

A Reynolds number is a dimensionless number used in the field of fluidmechanics. A Reynolds number (Re) can be calculated by the followingmathematical formula:

Re=ρvL/μ,

where, ρ represents the density of a fluid, v represents a speed of anobject, L represents a characteristic length, and μ represents aviscosity coefficient of the fluid.

As described above, the Reynolds number at the measurements of the liftcoefficient CL1 and the drag coefficient CD1 is 1.290×105. Regarding thegolf ball 2 which flies in the air, this Reynolds number corresponds toa ball speed when the golf ball 2 is launched with a driver at a headspeed of 35 m/s. The spin rate at the measurements of the liftcoefficient CL1 and the drag coefficient CD1 is 2820 rpm. This spin rateis an average value of a golf player having a head speed of 35 m/s. Formeasurement of the ratio L1, a golf player having a head speed of 35 m/sis assumed.

As described above, the Reynolds number at the measurements of the liftcoefficient CL2 and the drag coefficient CD2 is 1.771×105. Regarding thegolf ball 2 which flies in the air, this Reynolds number corresponds toa ball speed when the golf ball 2 is launched with a driver at a headspeed of 45 m/s. The spin rate at the measurements of the liftcoefficient CL2 and the drag coefficient CD2 is 2940 rpm. This spin rateis an average value of a golf player having a head speed of 45 m/s. Formeasurement of the ratio L2, a golf player having a head speed of 45 m/sis assumed.

Many amateur golf players have a head speed of equal to or greater than35 m/s but equal to or less than 45 m/s. In the above mathematicalformula (I), the ratio L1 corresponding to a head speed of 35 m/s andthe ratio L2 corresponding to a head speed of 45 m/s are averaged. Thegolf ball 2 in which an average value ((L1+L2)/2) is equal to or greaterthan 0.80 but equal to or less than 0.95 is suitable for many amateurgolf players.

When the golf ball 2 in which the average value ((L1+L2)/2) is equal toor greater than 0.80 is hit by an amateur golf player, a high trajectoryis achieved. Although the golf ball 2 conforms to the rules of the USGAabout flight distance, the golf player feels satisfied with thetrajectory. The golf ball 2 is excellent in trajectory feeling. In thisrespect, the average value ((L1+L2)/2) is more preferably equal to orgreater than 0.84 and particularly preferably equal to or greater than0.88.

The golf ball 2 in which the average value ((L1+L2)/2) is equal to orless than 0.95 is less likely to rise during flight. In this respect,the average value ((L1+L2)/2) is more preferably equal to or less than0.93 and particularly preferably equal to or less than 0.92.

The average value ((L1+L2)/2) can be achieved in the above range bymaking the specifications of the dimples 12 appropriate. Specifically,the ratio L1 and the ratio L2 can be made appropriate to achieve theaverage value ((L1+L2)/2) in the above range, by means such as:

(1) making the depth of each dimple 12 appropriate;

(2) making the area of each dimple 12 appropriate;

(3) making the volume of each dimple 12 appropriate;

(4) making the number of the dimples 12 appropriate;

(5) making the occupation ratio of the dimples 12 appropriate; and thelike.

The ratio L1 is preferably equal to or greater than 0.85 but equal to orless than 0.93. When the golf ball 2 having a ratio L1 of equal to orgreater than 0.85 is hit with a driver at a head speed of 35 m/s, a hightrajectory is achieved. Although the golf ball 2 conforms to the rulesof the USGA about flight distance, the golf player feels satisfied withthe trajectory. The golf ball 2 is excellent in trajectory feeling. Inthis respect, the ratio L1 is more preferably equal to or greater than0.87 and particularly preferably equal to or greater than 0.88. The golfball 2 having a ratio L1 of equal to or less than 0.93 is less likely torise during flight. In this respect, the ratio L1 is particularlypreferably equal to or less than 0.92.

The ratio L2 is preferably equal to or greater than 0.76 but equal to orless than 0.92. When the golf ball 2 having a ratio L2 of equal to orgreater than 0.76 is hit with a driver at a head speed of 45 m/s, a hightrajectory is achieved. Although the golf ball 2 conforms to the rulesof the USGA about flight distance, the golf player feels satisfied withthe trajectory. The golf ball 2 is excellent in trajectory feeling. Inthis respect, the ratio L2 is more preferably equal to or greater than0.80 and particularly preferably equal to or greater than 0.86. The golfball 2 having a ratio L2 of equal to or less than 0.92 is less likely torise during flight. In this respect, the ratio L2 is particularlypreferably equal to or less than 0.91.

EXAMPLES Example 1

A rubber composition was obtained by kneading 100 parts by weight of ahigh-cis polybutadiene (trade name “BR-730”, manufactured by JSRCorporation), 22.5 parts by weight of zinc diacrylate, 5 parts by weightof zinc oxide, an appropriate amount of barium sulfate, 0.5 parts byweight of diphenyl disulfide, and 0.6 parts by weight of dicumylperoxide. This rubber composition was placed into a mold including upperand lower mold halves each having a hemispherical cavity, and heated at170° C. for 18 minutes to obtain a center with a diameter of 38.5 mm.

A resin composition was obtained by kneading 50 parts by weight of anionomer resin (trade name “Himilan 1605”, manufactured by Du Pont-MITSUIPOLYCHEMICALS Co., Ltd.), 50 parts by weight of another ionomer resin(“Himilan AM7329”, manufactured by Du Pont-MITSUI POLYCHEMICALS Co.,Ltd.), and 4 parts by weight of titanium dioxide with a twin-screwkneading extruder. The center was covered with the resin composition byinjection molding to form a mid layer with a thickness of 1.6 mm.

A paint composition (trade name “POLIN 750LE”, manufactured by SHINTOPAINT CO., LTD.) including a two-component curing type epoxy resin as abase polymer was prepared. The base material liquid of this paintcomposition includes 30 parts by weight of a bisphenol A type solidepoxy resin and 70 parts by weight of a solvent. The curing agent liquidof this paint composition includes 40 parts by weight of a modifiedpolyamide amine, 55 parts by weight of a solvent, and 5 parts by weightof titanium dioxide. The weight ratio of the base material liquid to thecuring agent liquid is 1/1. This paint composition was applied to thesurface of the mid layer with a spray gun, and kept at 23° C. for 6hours to obtain a reinforcing layer with a thickness of 10 μm.

A resin composition was obtained by kneading 100 parts by weight of athermoplastic polyurethane elastomer (trade name “Elastollan XNY85A”,manufactured by BASF Japan Ltd.) and 4 parts by weight of titaniumdioxide with a twin-screw kneading extruder. Half shells were formedfrom this resin composition by compression molding. The sphereconsisting of the center, the mid layer, and the reinforcing layer wascovered with two of these half shells. The half shells and the spherewere placed into a final mold that includes upper and lower mold halveseach having a hemispherical cavity and having a large number of pimpleson its cavity face, and a cover was obtained by compression molding. Thethickness of the cover was 0.5 mm. Dimples having a shape that is theinverted shape of the pimples were formed on the cover. A clear paintincluding a two-component curing type polyurethane as a base materialwas applied to this cover to obtain a golf ball of Example 1 with adiameter of about 42.7 mm and a weight of about 45.6 g. The golf ballhas dimple specifications D3 shown in Table 1 below.

Examples 2 to 11 and Comparative Examples 1 to 9

Golf balls of Examples 2 to 11 and Comparative Examples 1 to 9 wereobtained in the same manner as Example 1, except the specifications ofthe center, the mid layer, the cover, and the dimples were as shown inTables 5 to 8 below. The composition of the center is shown in detail inTable 1 below. The compositions of the mid layer and the cover are shownin detail in Table 2 below. The specifications of the dimples are shownin detail in Tables 3 and 4 below.

[Flight Test]

A driver with a head made of a titanium alloy (trade name “XXIO”,manufactured by DUNLOP SPORTS CO. LTD., shaft hardness: R, loft angle:11°) was attached to a swing machine manufactured by Golf Laboratories,Inc. A golf ball was hit under a condition of a head speed of 40 msec,and a ball speed, a launch angle, a spin rate, highest point coordinates(x, y), and a carry were measured. The coordinate x is the horizontaldistance from the launch point to the highest point. The coordinate y isthe vertical distance from the launch point to the highest point. Thecarry is the distance from the launch point to the landing point. Theresults are shown in Tables 9 to 12 below.

[Sensuous Evaluation]

Ten testers hit golf balls with drivers and evaluated trajectory feelingand hit feeling. The evaluation was categorized on the basis of thefollowing criteria. The results are shown in Tables 9 to 12 below.

Trajectory feeling: the number of testers who feel that a flightdistance is long.

A: 8 or more

B: 5 to 7

C: 2 to 4

D: 1 or less

Hit feeling: the number of tester who feel soft.

A: 8 or more

B: 5 to 7

C: 2 to 4

D: 1 or less

TABLE 1 Composition of Center (parts by weight) T1 T2 T3 T4 T5 BR730 100100 100 100 100 Zinc 18.5 20.0 22.5 26.5 27.5 diacrylate Zinc oxide 5 55 5 5 Barium sulfate * * * * * Diphenyl 0.5 0.5 0.5 0.5 0.5 disulfideDicumyl 0.5 0.5 0.6 0.7 0.7 peroxide * Appropriate amount

TABLE 2 Compositions of Mid Layer and Cover (parts by weight) M1 C1 C2C3 C4 C5 Himilan #1605 50 Himilan AM7329 50 50 Himilan AM7337 24 RabalonT3221C 26 Barium sulfate 17 Elastollan XNY82A 100 Elastollan XNY85A 100Elastollan XNY90A 100 Elastollan XNY97A 100 Titanium dioxide 4 4 4 4 4 6Hardness (Shore D) 65 29 32 38 47 52

TABLE 3 Specifications of Dimples Number of Diameter Depth Volume Typedimples (mm) (mm) (mm³) D1 A 42 4.6 0.224 1.865 B 72 4.4 0.214 1.626 C66 4.2 0.183 1.272 D 126 4.0 0.164 1.030 E 12 3.9 0.149 0.892 F 12 2.60.100 0.265 D2 A 42 4.6 0.244 2.032 B 72 4.4 0.234 1.778 C 66 4.2 0.2031.411 D 126 4.0 0.184 1.156 E 12 3.9 0.169 1.011 F 12 2.6 0.120 0.318 D3A 42 4.6 0.264 2.198 B 72 4.4 0.254 1.931 C 66 4.2 0.223 1.550 D 126 4.00.204 1.282 E 12 3.9 0.189 1.131 F 12 2.6 0.140 0.371 D4 A 42 4.6 0.2742.282 B 72 4.4 0.264 2.007 C 66 4.2 0.233 1.619 D 126 4.0 0.214 1.345 E12 3.9 0.199 1.191 F 12 2.6 0.150 0.398

TABLE 4 Specifications of Dimples Number of Diameter Depth Volume Typedimples (mm) (mm) (mm³) D5 A 42 4.6 0.284 2.365 B 72 4.4 0.274 2.083 C66 4.2 0.243 1.689 D 126 4.0 0.224 1.408 E 12 3.9 0.209 1.251 F 12 2.60.160 0.425 D6 A 42 4.6 0.294 2.449 B 72 4.4 0.284 2.160 C 66 4.2 0.2531.759 D 126 4.0 0.234 1.471 E 12 3.9 0.219 1.311 F 12 2.6 0.170 0.451 D7A 42 4.6 0.334 2.783 B 72 4.4 0.324 2.466 C 66 4.2 0.293 2.038 D 126 4.00.274 1.724 E 12 3.9 0.259 1.551 F 12 2.6 0.210 0.559

TABLE 5 Specifications of Golf Ball Comp. Ex. 3 Ex. 1 Ex. 2 Ex. 3 Ex. 4Center Composition T3 T3 T3 T3 T3 Diameter 38.50 38.50 38.50 38.50 38.50H1 (D) 46 46 46 46 46 DF1 (mm) 5.05 5.05 5.05 5.05 5.05 Weight (g) 35.035.0 35.0 35.0 35.0 Mid Composition M1 M1 M1 M1 M1 layer Thickness 1.601.60 1.60 1.60 1.60 (mm) H2 (D) 65 65 65 65 65 Diameter 41.70 41.7041.70 41.70 41.70 Core DF2 (mm) 4.30 4.30 4.30 4.30 4.30 Weight (g) 43.443.4 43.4 43.4 43.4 Cover Composition C2 C2 C2 C2 C2 Thickness 0.50 0.500.50 0.50 0.50 (mm) H3 (D) 32 32 32 32 32 Ball Diameter 42.70 42.7042.70 42.70 42.70 DF3 (mm) 4.10 4.10 4.10 4.10 4.10 Weight (g) 45.6 45.645.6 45.6 45.6 Dimple Specifications D1 D2 D3 D4 D5 Total volume 423 468513 536 558 (mm³) CD1 0.311 0.287 0.274 0.238 0.233 CL1 0.301 0.2660.252 0.211 0.198 L1 0.968 0.928 0.918 0.887 0.852 CD2 0.255 0.243 0.2290.225 0.224 CL2 0.241 0.221 0.196 0.180 0.171 L2 0.945 0.912 0.860 0.8010.761 (L1 + L2)/2 0.956 0.920 0.889 0.844 0.806

TABLE 6 Specifications of Golf Ball Comp. Comp. Comp. Ex. 4 Ex. 5 Ex. 6Ex. 5 Ex. 6 Center Composition T3 T3 T1 T2 T4 Diameter 38.50 38.50 38.5038.50 38.50 H1 (D) 46 46 38 42 51 DF1 (mm) 5.05 5.05 6.05 5.75 4.05Weight (g) 35.0 35.0 35.0 35.0 35.0 Mid Composition M1 M1 M1 M1 M1 layerThickness 1.60 1.60 1.60 1.60 1.60 (mm) H2 (D) 65 65 65 65 65 Diameter41.70 41.70 41.70 41.70 41.70 Core DF2 (mm) 4.30 4.30 5.30 5.00 3.30Weight (g) 43.4 43.4 43.4 43.4 43.4 Cover Composition C2 C2 C2 C2 C2Thickness 0.50 0.50 0.50 0.50 0.50 (mm) H3 (D) 32 32 32 32 32 BallDiameter 42.70 42.70 42.70 42.70 42.70 DF3 (mm) 4.10 4.10 5.10 4.80 3.10Weight (g) 45.6 45.6 45.6 45.6 45.6 Dimple Specifications D6 D7 D3 D3 D3Total volume 581 672 513 513 513 (mm³) CD1 0.235 0.238 0.274 0.274 0.274CL1 0.197 0.169 0.252 0.252 0.252 L1 0.839 0.709 0.918 0.918 0.918 CD20.228 0.235 0.229 0.229 0.229 CL2 0.170 0.155 0.196 0.196 0.196 L2 0.7450.661 0.860 0.860 0.860 (L1 + L2)/2 0.792 0.685 0.889 0.889 0.889

TABLE 7 Specifications of Golf Ball Comp. Comp. Comp. Ex. 7 Ex. 8 Ex. 7Ex. 8 Ex. 9 Center Composition T5 T3 T3 T3 T3 Diameter 38.50 38.50 38.5038.50 38.50 H1 (D) 54 46 46 46 46 DF1 (mm) 3.85 5.05 5.05 5.05 5.05Weight (g) 35.0 35.0 35.0 35.0 35.0 Mid Composition M1 M1 M1 M1 M1 layerThickness 1.60 1.60 1.60 1.60 1.60 (mm) H2 (D) 65 65 65 65 65 Diameter41.70 41.70 41.70 41.70 41.70 Core DF2 (mm) 3.10 4.30 4.30 4.30 4.30Weight (g) 43.4 43.4 43.4 43.4 43.4 Cover Composition C2 C1 C3 C4 C5Thickness 0.50 0.50 0.50 0.50 0.50 (mm) H3 (D) 32 29 38 47 53 BallDiameter 42.70 42.70 42.70 42.70 42.70 DF3 (mm) 2.85 4.15 4.05 4.00 3.95Weight (g) 45.6 45.6 45.6 45.6 45.6 Dimple Specifications D3 D3 D3 D3 D3Total volume 513 513 513 513 513 (mm³) CD1 0.274 0.274 0.274 0.274 0.274CL1 0.252 0.252 0.252 0.252 0.252 L1 0.918 0.918 0.918 0.918 0.918 CD20.229 0.229 0.229 0.229 0.229 CL2 0.196 0.196 0.196 0.196 0.196 L2 0.8600.860 0.860 0.860 0.860 (L1 + L2)/2 0.889 0.889 0.889 0.889 0.889

TABLE 8 Specifications of Golf Ball Comp. Comp. Ex. 9 Ex. 10 Ex. 11 Ex.1 Ex. 2 Center Composition T3 T3 T3 T4 T4 Diameter 37.50 36.50 35.5038.50 38.50 H1 (D) 46 46 46 51 51 DF1 (mm) 5.05 5.05 5.05 4.05 4.05Weight (g) 32.3 29.8 27.4 35.0 35.0 Mid Composition M1 M1 M1 M1 M1 layerThickness 1.60 1.60 1.60 1.60 1.60 (mm) H2 (D) 65 65 65 65 65 Diameter40.70 39.70 38.70 41.70 41.70 Core DF2 (mm) 4.30 4.30 4.30 3.30 3.30Weight (g) 40.3 37.4 34.6 43.4 43.4 Cover Composition C4 C4 C4 C3 C3Thickness 1.00 1.50 2.00 0.50 0.50 (mm) H3 (D) 47 47 47 38 38 BallDiameter 42.70 42.70 42.70 42.70 42.70 DF3 (mm) 4.05 4.10 4.15 3.05 3.05Weight (g) 45.6 45.6 45.6 45.6 45.6 Dimple Specifications D3 D3 D3 D6 D7Total volume 513 513 513 581 672 (mm³) CD1 0.274 0.274 0.274 0.235 0.238CL1 0.252 0.252 0.252 0.197 0.169 L1 0.918 0.918 0.918 0.839 0.709 CD20.229 0.229 0.229 0.228 0.235 CL2 0.196 0.196 0.196 0.170 0.155 L2 0.8600.860 0.860 0.745 0.661 (L1 + L2)/2 0.889 0.889 0.889 0.792 0.685

TABLE 9 Results of Evaluation Comp. Ex. 3 Ex. 1 Ex. 2 Ex. 3 Ex. 4 Cover0.50 0.50 0.50 0.50 0.50 thickness (mm) Hardness H3 32 32 32 32 32 (D)Deformation 4.10 4.10 4.10 4.10 4.10 DF3 (mm) Total volume 423 468 513536 558 (mm³) L1 0.968 0.928 0.918 0.887 0.852 L2 0.945 0.912 0.8600.801 0.761 (L1 + L2)/2 0.956 0.920 0.889 0.844 0.806 Flight test Ballspeed 56.80 56.80 56.80 56.80 56.80 (m/s) Launch 12.5 12.5 12.5 12.512.5 angle (deg) Spin (rpm) 2850 2850 2850 2850 2850 Highest 102 107 111109 111 point (x) Highest 24 23 22 21 19 point (y) Carry (m) 162 166 168176 177 Feeling Trajectory C B A A B feeling Hit feeling A A A A A

TABLE 10 Results of Evaluation Comp. Comp. Comp. Ex. 4 Ex. 5 Ex. 6 Ex. 5Ex. 6 Cover 0.50 0.50 0.50 0.50 0.50 thickness (mm) Hardness H3 32 32 3232 32 (D) Deformation 4.10 4.10 5.10 4.80 3.10 DF3 (mm) Total volume 581672 513 513 513 (mm³) L1 0.839 0.709 0.918 0.918 0.918 L2 0.745 0.6610.860 0.860 0.860 (L1 + L2)/2 0.792 0.685 0.889 0.889 0.889 Flight testBall speed 56.80 56.80 55.70 56.30 57.45 (m/s) Launch 12.5 12.5 12.812.7 12.4 angle (deg) Spin (rpm) 2850 2850 2700 2750 2900 Highest 113107 107 107 111 point (x) Highest 18 17 21 22 23 point (y) Carry (m) 179173 164 166 170 Feeling Trajectory C D A A A feeling Hit feeling A A C BB

TABLE 11 Results of Evaluation Comp. Comp. Comp. Ex. 7 Ex. 8 Ex. 7 Ex. 8Ex. 9 Cover 0.50 0.50 0.50 0.50 0.50 thickness (mm) Hardness 32 29 38 4753 H3 (D) Deformation 2.85 4.15 4.05 4.00 3.95 DF3 (mm) Total volume 513513 513 513 513 (mm³) L1 0.918 0.918 0.918 0.918 0.918 L2 0.860 0.8600.860 0.860 0.860 (L1 + L2)/2 0.889 0.889 0.889 0.889 0.889 Flight testBall speed 57.55 56.75 56.85 56.90 56.95 (m/s) Launch 12.3 12.3 13.113.4 13.5 angle (deg) Spin (rpm) 2950 2950 2550 2400 2350 Highest 111108 109 112 114 point (x) Highest 23 22 22 22 22 point (y) Carry (m) 170165 171 175 178 Feeling Trajectory A C A A A feeling Hit feeling D A A AA

TABLE 12 Results of Evaluation Comp. Comp. Ex. 9 Ex. 10 Ex. 11 Ex. 1 Ex.2 Cover 1.00 1.50 2.00 0.50 0.50 thickness (mm) Hardness 47 47 47 38 38H3 (D) Deformation 4.05 4.10 4.15 3.05 3.05 DF3 (mm) Total volume 513513 513 581 672 (mm³) L1 0.918 0.918 0.918 0.839 0.709 L2 0.860 0.8600.860 0.745 0.661 (L1 + L2)/2 0.889 0.889 0.889 0.792 0.685 Flight testBall speed 56.85 56.80 56.75 57.50 57.50 (m/s) Launch 13.0 12.8 12.713.0 13.0 angle (deg) Spin (rpm) 2600 2700 2750 2600 2600 Highest 111110 108 115 108 point (x) Highest 22 22 22 19 18 point (y) Carry (m) 169168 166 183 176 Feeling Trajectory A A B A D feeling Hit feeling A A B CC

As shown in Tables 9 to 12, the golf ball of each Example is excellentin various performance characteristics. From the results of evaluation,advantages of the present invention are clear.

The golf ball according to the present invention is suitable for, forexample, playing golf on golf courses and practicing at driving ranges.The above descriptions are merely illustrative examples, and variousmodifications can be made without departing from the principles of thepresent invention.

What is claimed is:
 1. A golf ball comprising a center, a mid layerpositioned outside the center, and a cover positioned outside the midlayer, wherein the golf ball has a large number of dimples on a surfacethereof, the center has an amount of compressive deformation of equal toor greater than 4.05 mm but equal to or less than 6.5 mm, the amount ofcompressive deformation being measured under conditions of an initialload of 98 N and a final load of 1274 N, the mid layer has a shore Dhardness of equal to or greater than 55 but equal to or less than 75,the cover has a Shore D hardness of equal to or greater than 30 butequal to or less than 40, the golf ball has an amount of compressivedeformation of equal to or greater than 3.10 mm but equal to or lessthan 5.0 mm, the amount of compressive deformation being measured underconditions of an initial load of 98 N and a final load of 1274 N, andthe golf ball meets the following mathematical formula:0.806=((L1+L2)/2)=0.920, where: L1 represents a ratio (CL1/CD1) of alift coefficient CL1 relative to a drag coefficient CD1, the liftcoefficient CL1 and the drag coefficient CD1 being measured underconditions of a Reynolds number of 1.290×105 and a spin rate of 2820rpm; and L2 represents a ratio (CL2/CD2) of a lift coefficient CL2relative to a drag coefficient CD2, the lift coefficient CL2 and thedrag coefficient CD2 being measured under conditions of a Reynoldsnumber of 1.771×105 and a spin rate of 2940 rpm.
 2. The golf ballaccording to claim 1, wherein a total volume of the dimples is equal toor greater than 430 mm3 but equal to or less than 580 mm3.
 3. The golfball according to claim 1, wherein the cover has a thickness of equal toor greater than 0.3 mm but equal to or less than 1.8 mm.
 4. The golfball according to claim 1, wherein the ratio L1 is equal to or greaterthan 0.85 but equal to or less than 0.93.
 5. The golf ball according toclaim 1, wherein the ratio L2 is equal to or greater than 0.76 but equalto or less than 0.92.
 6. The golf ball according to claim 1, wherein aratio of a sum of spherical surface areas of the dimples relative to asurface area of a phantom sphere of the golf ball is equal to or greaterthan 0.780 but equal to or less than 0.950.
 7. The golf ball accordingto claim 1, wherein a total number of the dimples is equal to or greaterthan 250 but equal to or less than
 450. 8. The golf ball according toclaim 1, wherein each dimple has a diameter Dm of equal to or greaterthan 2.0 mm but equal to or less than 6.0 mm.
 9. The golf ball accordingto claim 1, wherein each dimple has a depth of equal to or greater than0.10 mm but equal to or less than 0.60 mm.